The prevalence of overweight and obesity among children and adolescents is increasing. Alarmingly, overweight and obese children are experiencing weight-related health problems before adulthood, such as type 2 diabetes mellitus. Weight gain and obesity are the consequence of a positive energy balance, which occurs when more energy is ingested than expended, and energy intake is an important predictor of weight gain. The types of foods that children and adolescents eat also affect health. Children and adolescents consume over 500 kcal/day of low-nutrient, energy dense foods, and nutritional deficiency can occur even in the presence of overconsumption of energy. For example, obese children have higher rates of iron deficiency. Accurate methods to measure the food intake of children and adolescents are needed to facilitate research and interventions to promote healthy eating and weight management. Existing methods, such as self- report (e.g., food records), are associated with significant participant and, with younger children, caregiver burden. Moreover, these methods produce inaccurate (low) estimates of food intake, particularly for people of higher body mass and adolescents. A large source of error when using these methods is due to participants' poor estimation of portion size. Hence, there is a need to develop and validate methods to estimate the food intake of children, namely adolescents that do not rely on the participant's ability to accurately estimate portion size. Our group developed the Remote Food Photography Method (RFPM) for measuring the food intake of adults in near real-time, and the validity data are positive. The RFPM underestimated energy intake by less than 7% over 7 days in free-living conditions when compared to the gold standard, doubly labeled water. When utilizing the RFPM, participants use a Smartphone to take pictures of their food selection and plate waste. These pictures are immediately sent to the researchers via a wireless network. Participants receive automated prompts (emails) on the Smartphone that are consistent with Ecological Momentary Assessment (EMA) methodology reminding them to take pictures of their foods. Computer applications were developed to manage EMA methods and to automatically identify foods and estimate food intake using computer imaging algorithms. Data are collected and analyzed quickly and efficiently, allowing near real-time food intake measurement. During the proposed research, the RFPM will be modified to measure the food intake of adolescents. The validity of the RFPM will then be compared to the validity of pen-and-paper food records. Following modification of the RFPM and pilot testing with 4 adolescents, the reliability and validity of the RFPM and food records will then be tested in a sample of 64 adolescents (age 12-18 years). In a balanced order across participants, the RFPM will be used during one week, and food records will be used during another week. Food intake estimated with both methods will be compared to three gold standards: 1) energy intake measured by doubly labeled water (DLW) in free-living conditions, 2) food intake (energy and nutrient intake) measured during lunch in a school cafeteria, and 3) food intake measured during a laboratory-based test meal. User satisfaction and burden also will be compared between methods (RFPM and food records), and a cost- effectiveness analysis will determine if and under what conditions one method is more cost-effective than the other. We will also test if the RFPM's validity is associated with levels of energy intake.